This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 2002-266143 filed in Japan on Sep. 11, 2002, the entirety of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an engine fuel injection apparatus. More more particularly, the present invention relates to an improved engine fuel injection apparatus.
2. Description of Background Art
Japanese Patent Document No. JP-A-2000-97132 (P.3-4, FIGS. 1-3) describes and shows a motorcycle having an engine fuel injection apparatus of the background art. This type of engine fuel injection apparatus includes a first fuel injection valve provided on an upstream side of an engine throttle valve, and a second fuel injection valve provided on a downstream side of the throttle valve. In addition, fuel is supplied to the first and the second fuel injection valves by a fuel pump.
However, the present inventors have determined that the apparatus of the background art suffers from the following disadvantages. For example, a fuel feed pipe from the fuel pump is branched and connected to the first fuel injection valve and the second fuel injection valve, respectively, and excess fuel is returned to a fuel tank from the first and the second fuel injection valves via a return pipe. Therefore, an increased number of pipes in the fuel piping and coupling parts is required with this apparatus of the background art. Furthermore, assembly is more time consuming and is limited in the order in which the respective parts may be installed or connected. Therefore, piping work, maintenance, and inspection are cumbersome in the apparatus of the background art.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art. An object of the present invention is to provide an improved fuel injection apparatus that can reduce the required number of pipes and coupling parts in the fuel system.
An additional object of the present invention is to provide an improved fuel injection apparatus that facilitates piping work, maintenance, and inspection.
In order to achieve the object, a first aspect of the present invention is directed to an engine fuel injection apparatus including a first fuel injection valve provided on an upstream side of an air intake passage of an engine, a second fuel injection valve provided on a downstream side of the air intake passage, and a fuel pump for supplying fuel to the first and the second fuel injection valves, wherein the fuel pump is connected to the second fuel injection valve via the first fuel injection valve or to the first fuel injection valve via the second fuel injection valve by a fuel feed pipe, so that fuel does not return to a fuel tank.
The fuel pump is connected to the second fuel injection valve via the first fuel injection valve or to the first fuel injection valve via the second fuel injection valve by the fuel feed pipe, so that fuel does not return to the fuel tank. Accordingly, a return pipe is not necessary and thus the number of fuel feed pipes may be reduced correspondingly. The number of joints (joint parts) of the fuel feed pipes may also be reduced. Therefore, fuel piping can be simplified. In addition, since maintenance and inspection are facilitated, the workability is improved.
According to a second aspect of the present invention, the fuel pump is connected to the second fuel injection valve via the first fuel injection valve by the fuel feed pipe, the first fuel injection valve is a fuel injection valve for high-speed operation that injects fuel when the number of revolutions of the engine is high, and the second fuel injection valve is a fuel injection valve for low-speed operation that injects fuel when the number of revolutions of the engine is low.
While the engine is in operation, fuel is constantly injected from the second fuel injection valve for low-speed operation. Therefore, even when a small quantity of air is mixed in the fuel in the fuel piping, it is injected in an early stage and constantly from the second fuel injection valve. Therefore, the quantity of air trapped in the first fuel injection valve for high-speed operation is negligible, and thus the engine can maintain a stable performance.
According to a third aspect of the present invention, the fuel pump is connected to the first fuel injection valve via the second fuel injection valve and the first fuel injection valve is disposed at a level higher than the second fuel injection valve by the fuel feed pipe.
Fuel is supplied to the second fuel injection valve, which is located at a lower level on ahead. When the engine is in operation, fuel is constantly injected from the second fuel injection valve, which is located at the lower level. Therefore, even when a small quantity of air is mixed in the fuel in the fuel piping, it is injected in an earlier stage and constantly from the second fuel injection valve. Consequently, the quantity of air trapped in the first fuel injection valve located at a higher level is negligible, and thus the engine can maintain its performance in a more stable manner.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.